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American Society of Landscape Architects

 

October 2007 Issue

Research Design Connections
Studies examine what makes good pedestrian spaces, the impacts of insects on trees, and whether greenways welcome birds.

By Sally Augustin and Jean Marie Cackowski-Campbell, ASLA

Research Design Connections William Brown

Landscape Architecture, in partnership with the web-based newsletter and daily blog Research Design Connections, uses this column to report current research of interest to landscape architects from a wide array of disciplines. We welcome your comments, suggestions about future topics, and studies you have encountered in your own practice.

Will Pedestrians Enjoy This Space?

Will a space you are developing to encourage walking please pedestrians? Use a new questionnaire and find out. Both practitioners and academics can employ the Pedestrian Environmental Data Scan (PEDS), a new environmental audit developed by Kelly Clifton, Andrea Smith, and Daniel Rodriguez, to assess aspects of the physical environment experienced by people who walk and bike (or use other nonmotorized transportation). They have designed the audit to specifically include characteristics not addressed by existing tools that relate features of the physical environment to modes of transportation.

The developers of the PEDS instrument designed it to collect information efficiently and reliably; testing has shown that laypeople can accurately administer the audit to assess both the built and natural environments. It can be conducted either on paper or in digital form, integrated with handheld technology. A comprehensive training package is available. The release of this instrument now is particularly advantageous because of current attention to the link between the design of the physical environment and resulting levels of physical activity.

Its developers selected the features of the physical environment in the PEDS assessment after weighing competing needs for detailed information and efficiency during use—one of the features distinguishing the PEDS audit from predecessors. The paper version is one page long. The audit contains a total of 40 questions in five main categories: macroscale environment, pedestrian facilities, road attributes, microscale features of the environment, and the administrator’s subjective impressions of the overall quality of the walking (and cycling) environment. (The authors use the terms “administrator,” “auditor,” and “rater” interchangeably to mean “user.”)

The instrument allows the person conducting the audit to define the size and type of the area being audited. For example, a segment might be defined as the area between intersections, or it might be based on more subjective definitions. The authors do state, however: “Segments are generally defined as a road or pedestrian path bounded by cross streets or intersections. These segments are identified using secondary street or pedestrian network layers in a geographic information systems software platform. In cases where segments are longer than 700 feet, the segment is subdivided to ensure consistency in the segment length and for better comparison of variation across segments.” (Segment length and block length do not necessarily coincide.) Auditors simultaneously evaluate both sides of a street unless there is some obstacle preventing easy movement from one side to the other, in which case they assess each side independently.

The comprehensive training available for PEDS users includes materials and protocols that extensively define the application and response options. For example, the response options for the “uses in segment” question define the response “office/institutional” as “office parks, corporate campuses, public buildings, schools, churches, hospitals, etc.”

For those who prefer to perform the audit digitally, as opposed to with pencil and paper, the PEDS has been tested for reliability of use on personal digital assistants (PDAs). Entering information directly into a PDA eliminates a separate data-entry step and streamlines the process of completing the audit, because all required materials (maps, protocols) are loaded directly into the PDA.

Testing by the developers indicates that administrators who are walking complete the PEDS for a segment of 400 feet, on average, in three to five minutes. The authors note, however: “When training and reliability testing are included, the labor investment for PEDS increases to 10 to 12 minutes per segment per rater.” Using a PDA reduces administration time by two minutes per segment, on average.

In summary, the developers write: “The instrument and methodology can be employed in all of these built environments [urban, suburban, and rural] and can capture differences in the features of the pedestrian environment in each type. PEDS is not an appropriate tool for assessing recreational or hiking trails in rural or wilderness settings.”

For more information about obtaining PEDS and/or training for the system, contact lead author Kelly Clifton at kclifton@umd.edu.

Source

  • “The Development and Testing of an Audit for the Pedestrian Environment,” by Kelly Clifton, Andrea Smith, and Daniel Rodriguez; Landscape and Urban Planning, vol. 80, 2007.

Is Insect Damage Always Ugly?

People can find red treetops beautiful—even when it’s not autumn, and the off-season color is caused by beetle damage. Stephen Sheppard, ASLA, and Paul Picard review related published research to determine the visual ramifications of insect infestations.

Although some researchers have found that the general public feels the loss of scenic beauty is one of the most significant impacts of infestations, the authors of this study conclude, “Visual-quality ratings generally decrease significantly as pest damage increases in the middle ground landscape...[but] reductions in visual quality due to pest attack may be outweighed by high visual quality of the overall scene. Low levels of beetle damage may even enhance the visual quality of a landscape temporarily.”

Particularly for the most scenic views, some beetle infestations, manifested as a change in leaf color, for example, appear to have only a slight impact on the visual quality of a scene.

The threshold for visible beetle damage appears to be about 10 percent of the visible forested area; at this point participants’ visual-quality ratings show less response as pest damage increases incrementally.

Source

  • “Visual-Quality Impacts of Forest Pest Activity at the Landscape Level: A Synthesis of Published Knowledge and Research Needs,” by Stephen Sheppard, ASLA, and Paul Picard; Landscape and Urban Planning, vol. 77, 2006.  

Which Suburban Greenways Really Work for Birds?

Researchers have established that suburban greenways can provide valuable habitat for forest-breeding birds. Now a study by James Mason, Christopher Moorman, George Hess, and Kristen Sinclair has quantified how width, habitability, adjacent land use, and cover affect the viability of greenways as bird habitat.

Research conducted in Raleigh and Cary, North Carolina, over two years investigated the appropriate greenway widths for neotropical migrants, insectivores, and forest-interior specialist birds. (The authors define “greenways” as “linear protected lands composed of natural vegetation, or at least vegetation that is more natural than in surrounding areas.”) The study also examined the influence of the type and amount of vegetation and adjacent land use on the abundance and assortment of breeding birds found there.

The study area in North Carolina is both urban and suburban. As the area is becoming more populated, man-made environments are replacing forests and fields. The authors sampled birds in 34 300-meter-long segments of publicly owned mature forest in riparian greenways, each at least 75 meters apart. In measuring greenway width, the researchers included the width of the forested area on both sides of the stream, as well as the width of the stream. The study segments they selected remained relatively the same width throughout the entire segment, and the land use on both sides of the sections studied was similar. They conducted bird counts at the midpoints of the 300-meter study segments.

The researchers also precisely defined several key terms: Short-distance migrant birds, for example, are those that have winter ranges that don’t include the study area but do include some portion of the southeastern United States. Development-sensitive species were, for the purposes of this study, defined as neotropical migrants, insectivores, or birds that live in interior forests. Mature forests, in this context, are areas covered with trees taller than six meters. Managed areas were defined to include mowed and otherwise maintained surfaces, roads, parks, trails, and ball fields.

The researchers calculated total species richness for each greenway segment as the total number of bird species recorded each year; richness was similarly calculated for each bird species. Abundance of individual species was defined as the average number of adult males of a species recorded during all visits in a year. The researchers visited each of the 34 sites 6 times over the course of the project.

Among the forest-interior species they observed were Acadian flycatchers, hairy woodpeckers, red-shouldered hawks, and wood thrushes. Interior-edge species included blue-gray gnatcatchers, Carolina chickadees, Carolina wrens, downy woodpeckers, tufted titmice, great crested flycatchers, northern cardinals, red-bellied woodpeckers, red-eyed vireos, and white-breasted nuthatches. The edge species they observed included American crows, American goldfinches, American robins, blue jays, common grackles, eastern towhees, gray catbirds, and northern flickers.

The researchers determined that the amount of managed area had the most consistent impact on species richness and abundance, negatively influencing the richness of species overall, and, more specifically, the richness and abundance of the neotropical, insectivore, and forest-interior species. In addition, as the percentage of hardwood tree species in the area increased, the overall bird and insectivore richness and abundance decreased. As streams became wider, the abundance of neotropical birds and the richness of the forest-interior species increased. As the percent of adjacent land covered by pavement and bare earth increased, total bird abundance and neotropical migrant bird richness decreased, as did the richness and abundance of insectivores. As buildings covered more of the adjacent areas, neotropical migrant species declined in richness and abundance.

The width of the greenways proved to be quite significant. The study recorded no forest-interior species present in greenways less than 50 meters wide, and Acadian flycatchers, hairy woodpeckers, and wood thrushes were most abundant in greenways wider than 100 meters. Black-and-white warblers, Louisiana waterthrushes, ovenbirds, prothonotary warblers, scarlet tanagers, and yellow-throated warblers were spotted only in greenways wider than 300 meters. Blue-gray gnatcatchers, downy woodpeckers, and red-eyed vireos were most common in wider greenways. The white-eyed vireo was noted only in greenways wider than 300 meters and the indigo bunting in those wider than 100 meters. European starlings, house finches, house wrens, and mourning doves were the most common species sighted in greenways less than 50 meters wide. Red-shouldered hawks, northern flickers, and red-bellied woodpeckers were least abundant in greenways adjacent to office or institutional land, but the reverse was true for American crows.

For designers of greenways, the authors have some suggestions:

  • Place “greenway trails along one edge of a wide forested corridor, rather than directly down the middle of the corridor, [to minimize] the effect of greenway trail management and edge on ‘interior’ forest.”
  • Design trails narrow enough so that the forest canopy remains unbroken.
  • Mow areas less frequently, keep some greenway trails unpaved, and create greenways 300 to 600 meters wide, but “[w]hen greenways of this width are not realistic, larger, nonlinear reserves are needed to provide habitat for [forest-interior specialists and ground-nesting songbirds]. These might be located as ‘nodes’ along greenways.”

Source

  • “Designing Suburban Greenways to Provide Habitats for Forest-Breeding Birds,” by James Mason, Christopher Moorman, George Hess, and Kristen Sinclair; Landscape and Urban Planning, vol. 80, 2007.

Sally Augustin, RDC’s senior editor, is an environmental psychologist. Jean Marie Cackowski-Campbell, ASLA, is the publisher of Research Design Connections and has an MLA degree from Ohio State University.

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